Reactor and process for preparing polyolefin

ABSTRACT

The invention relates to a process for preparing polyolefin in a loop reactor. The polymer is prepared by polymerizing olefin monomers in the presence of a catalyst to produce a polyolefin slurry while pumping said slurry through said loop reactor by means of a pump. The present process is characterized in that the catalyst is fed in the loop reactor at a distance to the pump. The invention allows production of the polymer with advantageous properties while leading to fewer blockages of the reactor.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method of preparing polyolefin and toa loop reactor.

BACKGROUND OF THE INVENTION

Polyolefins, such as polyethylene (PE), are synthesized by polymerizingmonomers, such as ethylene (CH₂═CH₂). Because it is cheap, safe, stableto most environments and easy to be processed polyolefins are useful inmany applications. Polyethylene can be classified into several types,such as but not limited to LDPE (Low Density Polyethylene), LLDPE(Linear Low Density Polyethylene), and HDPE (High Density Polyethylene)as well as High Molecular Weight (HMW), Medium Molecular Weight (MMW)and Low Molecular Weight (LMW). Each type of polyethylene has differentproperties and characteristics.

Olefin (such as ethylene) polymerizations are frequently carried out ina loop reactor using monomer (such as ethylene), diluent and catalyst,optionally an activating agent, optionally one or more co-monomer(s),and optionally hydrogen.

Polymerization in a loop reactor is usually performed under slurryconditions, with the produced polymer usually in a form of solidparticles suspended in diluent. The slurry is circulated continuously inthe reactor with a pump to maintain efficient suspension of the polymersolid particles in the liquid diluent. Polymer slurry is discharged fromthe loop reactor by means of settling legs, which operate on a batchprinciple to recover the slurry. Settling in the legs is used toincrease the solid concentration of the slurry finally recovered asproduct slurry. The product slurry is further discharged through heatedflash lines to a flash tank, where most of the diluent and unreactedmonomers are flashed off and recycled.

Optionally, the product slurry may be fed to a second loop reactorserially connected to the first loop reactor wherein a second polymerfraction may be produced. Typically, when two reactors in series areemployed in this manner, the resultant polymer product is a bimodalpolymer product, which comprises a first polymer fraction produced inthe first reactor and a second polymer fraction produced in the secondreactor, and has a bimodal molecular weight distribution.

After the polymer product is collected from the reactor and thehydrocarbon residues are removed, the polymer product is dried,additives can be added and finally the polymer may be mixed andpelletized.

During the mixing step, polymer product and optional additives are mixedintimately in order to obtain a compound as homogeneous as possible.Preferably, mixing is done in an extruder wherein the ingredients aremixed together and the polymer product and optionally some of theadditives are melted so that intimate mixing can occur. The melt is thenextruded into a rod, cooled and granulated, e.g. to form pellets. Inthis form the resulting compound can then be used for the manufacturingof different objects.

Production of polyolefin involves the polymerization of olefin monomerin the reactor in the presence of a catalyst and optionally, if requireddepending on the used catalyst, an activating agent. Typically, thecatalyst is used in particulate form. The polyolefin is produced as aresin/powder with a hard catalyst particle at the core of each grain ofthe powder.

We have found that production of polyolefin can lead to complicationssuch as partial—or even complete—blockage of the loop reactor. Theseproblems can be even more pronounced with particular polyolefins, suchas polyethylenes. Blockage may require stopping the production processand unclogging and cleaning the reactor before production can berestarted. In view of the above, there remains a need in the art for animproved polyolefin production process, particularly for polyethyleneand the present invention aims to provide such improvements.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to reactors and processesfor improving the preparation of polyolefin. According to a first aspectof the present invention, a process of preparing polyolefin in a loopreactor is provided by:

-   -   (a) feeding into said loop reactor diluent, olefin monomers,        optionally one or more comonomers, and optionally hydrogen;    -   (b) feeding into said loop reactor a catalyst and optionally an        activating agent; and    -   (c) polymerizing said olefin monomers to produce a polyolefin        slurry comprising diluent and solid polyolefin particles while        pumping said slurry through said loop reactor by means of a        pump,

characterized in that the catalyst is fed into said loop reactorspatially separated from said pump and at a distance upstream to thepump of at least 20% of the length of the reactor path.

According to a second aspect, the present invention also encompasses aloop reactor suitable for the polymerization of olefin monomer, whereinsaid reactor is configured to perform the process according to the firstaspect of the invention and wherein said reactor comprises:

-   -   a plurality of interconnected pipes defining a reactor path for        a polymer slurry, said polymer slurry comprising monomer,        diluent, a catalyst, solid olefin polymer particles, optionally        one or more co-monomer(s), optionally hydrogen, and optionally        an activating agent;    -   means for feeding monomer, diluent, optionally one or more        co-monomer(s) and optionally hydrogen in the reactor;    -   means for feeding catalyst in the reactor;    -   optionally means for feeding an activating agent in the reactor;        and    -   a pump suitable for maintaining the polymer slurry in        circulation in said reactor,

characterized in that said means for feeding said catalyst in thereactor is spatially separated from the pump with a distance upstream tothe pump of at least 20% of the length of the reactor path.

The present inventors have found that the process and reactor accordingto the invention allow production of polyolefin with fewer problemsrelated to blockage and that subsequently can be easily extruded andthat has favorable properties.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 schematically illustrates a loop reactor that can be used in thepreparation of the polyethylene according to an embodiment of thepresent invention.

FIG. 2 schematically illustrates a double loop reactor that can be usedin the preparation of the polyethylene according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Before the present method and products of the invention are described,it is to be understood that this invention is not limited to particularmethods, components, products or combinations described, as suchmethods, components, products and combinations may, of course, vary. Itis also to be understood that the terminology used herein is notintended to be limiting, since the scope of the present invention willbe limited only by the appended claims.

As used herein, the singular forms “a”, “an”, and “the” include bothsingular and plural referents unless the context clearly dictatesotherwise.

The terms “comprising”, “comprises” and “comprised of” as used hereinare synonymous with “including”, “includes” or “containing”, “contains”,and are inclusive or open-ended and do not exclude additional,non-recited members, elements or method steps. It will be appreciatedthat the terms “comprising”, “comprises” and “comprised of” as usedherein comprise the terms “consisting of”, “consists” and “consists of”.

The recitation of numerical ranges by endpoints includes all numbers andfractions subsumed within the respective ranges, as well as the recitedendpoints.

The term “about” or “approximately” as used herein when referring to ameasurable value such as a parameter, an amount, a temporal duration,and the like, is meant to encompass variations of +/−10% or less,preferably +/−5% or less, more preferably +/−1% or less, and still morepreferably +/−0.1% or less of and from the specified value, insofar suchvariations are appropriate to perform in the disclosed invention. It isto be understood that the value to which the modifier “about” refers isitself also specifically, and preferably, disclosed.

All documents cited in the present specification are hereby incorporatedby reference in their entirety.

Unless otherwise defined, all terms used in disclosing the invention,including technical and scientific terms, have the meaning as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. By means of further guidance, term definitions are included tobetter appreciate the teaching of the present invention.

In the following passages, different aspects of the invention aredefined in more detail. Each aspect so defined may be combined with anyother aspect or aspects unless clearly indicated to the contrary. Inparticular, any feature indicated as being preferred or advantageous maybe combined with any other feature or features indicated as beingpreferred or advantageous.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present invention. Thus, appearances of the phrases“in one embodiment” or “in an embodiment” in various places throughoutthis specification are not necessarily all referring to the sameembodiment, but may. Furthermore, the particular features, structures orcharacteristics may be combined in any suitable manner, as would beapparent to a person skilled in the art from this disclosure, in one ormore embodiments. Furthermore, while some embodiments described hereininclude some but not other features included in other embodiments,combinations of features of different embodiments are meant to be withinthe scope of the invention, and form different embodiments, as would beunderstood by those in the art. For example, in the following claims,any of the claimed embodiments can be used in any combination.

The present invention relates to a process of preparing polyolefin in aloop reactor, preferably polyethylene, comprising:

-   -   (a) feeding into said loop reactor diluent, olefin monomers,        optionally one or more comonomers, and optionally hydrogen;    -   (b) feeding into said loop reactor a catalyst and optionally an        activating agent; and    -   (c) polymerizing said olefin monomers to produce a polyolefin        slurry comprising diluent and solid polyolefin particles while        pumping said slurry through said loop reactor by means of a        pump,

characterized in that the catalyst is fed into said loop reactorspatially separated from said pump and at a distance upstream to thepump of at least 20% of the length of the reactor path, more preferablyat least 30%, most preferably at least 40%, more preferably at least50%, at least 60%, at least 70%, at least 80%, at least 90%, at least95% of the length of the reactor path.

The pump is usually provided in the loop reactor in an elbow section ofa pipe, provides with flanges at each end, and said elbow section isoperably connected to the next segments by flanges. The impeller pushesthe liquid in a direction parallel to the pump shaft toward the outletof the elbow section. In an embodiment, the catalyst may be injected atany distance upstream to the pump of at least 20% of the length of thereactor path, up to the outlet flange of the pump.

Preferably the process is performed in a double loop reactor.

Polymers with a bimodal or multimodal molecular weight distribution maybe produced. By the term “polymers with a bimodal molecular weightdistribution” or “bimodal polymers” it is meant, polymers having twomaxima in their molecular weight distribution curves. By the term“polymers with a multimodal molecular weight distribution” or“multimodal” polymers it is meant polymers with at least two, preferablyabove two maxima in their molecular weight distribution curves.Preferably, the polyolefin is polyethylene, preferably bimodalpolyethylene.

Preferably, the polyethylene has an HLMI of larger than 0.015 g/10 min,more preferably larger than 0.03 g/10 min, most preferably larger than0.06 g/10 min and preferably smaller than 12 g/10 min, more preferablysmaller than 6.25 g/10 min, most preferably smaller than 2 g/10 min.

Preferably, said polyolefin, preferably polyethylene, has an HLMI offrom 0.015 to 12 g/10 min and a density of from 0.915 to 0.945 g/cm³.

The HLMI is determined with the ASTM D-1238 standardized test whichmeasures HL275 at a temperature of 190° C. and under a load of 21.6 kg,except that a die of 2.75 mm broad instead of 2.05 mm was used andwherein HLMI=HL275/3.2. The HLMI is preferably determined afterproduction of the fraction in the reactor (i.e. fluff) and/or beforesubsequent processing in dryers and extruders (i.e. pellets). In case ofbimodal polymer distributions, the HLMI may be determined by measuringone or more of the fractions and/or the bimodal polymer end product andusing the following formula:

Log HLMI_(final)=wt %_(1st)×Log HLMI_(1st)+wt %_(2nd)×Log HLMI_(2nd)

wherein

-   -   “final” means “of the polyethylene resin”    -   “1st” means “of the polyethylene fraction produced in the first        reactor”    -   “2nd” means “of the polyethylene fraction produced in the second        reactor, downstream of the first reactor”

Preferably, the polyethylene from the reactor has a density of largerthan 0.915 g/cm³, more preferably larger than 0.920 g/cm³ and preferablysmaller than to 0.945 g/cm³, more preferably smaller than 0.940 g/cm³.The density is determined with the ASTM D-1505 standardized test at atemperature of 23° C. The density is preferably determined afterproduction of the fraction in the reactor (i.e. fluff) and/or beforesubsequent processing in dryers and/or extruders (i.e. pellets). In caseof bimodal polymer distributions, the density may be determined bymeasuring one or more of the fractions and/or the bimodal polymer endproduct and using the following formula:

density_(final)=wt %_(1st)×density_(1st)+wt %_(2nd)×density_(2nd)

wherein

-   -   “final” means “of the polyethylene resin”    -   “1st” means “of the polyethylene fraction produced in the first        reactor”    -   “2nd” means “of the polyethylene fraction produced in the second        reactor, downstream of the first reactor”

In an embodiment, the polyolefin of the present the invention arepreferably combined with one or more other polyolefin fractions into abimodal distribution.

In a preferred embodiment, the polyolefin is bimodal polyethylene,prepared in a double loop reactor.

The polyolefin, particularly the polyethylene, of the invention isuseful for all application, such as pipes, and all resins applications,for example, for pipe, blow molding or film applications.

The polyolefin is prepared by feeding diluent, olefin monomers,optionally one or more co-monomers, and optionally hydrogen into theloop reactor. Catalyst and optionally activating agent are fed into theloop reactor creating a slurry. Said slurry is circulated through theloop reactor by means of a pump. The olefin monomers are polymerized toproduce a polyolefin slurry comprising diluent and solid polyolefinparticles while circulating said slurry through said loop reactor bymeans of a pump. The process is further characterized in that thecatalyst is fed into said loop reactor spatially separated from saidpump and at a distance upstream to the pump of at least 20% of thelength of the reactor path, for example at least 30%, for example atleast 40%, for example at least 50%, at least 60%, at least 70%, atleast 80%, at least 90%, at least 95%, of the length of the reactorpath.

Polymerization of olefin is preferably carried out in a loop reactor byfeeding olefin monomers (preferably ethylene), optionally a co-monomer(such as hexene-1), diluent (such as isobutane), a catalyst, optionallya activating agent and optionally hydrogen to a loop reactor. Apreferred process feeds olefin monomer into the loop reactor in step a)at a temperature of lower than 15° C. and preferably at a temperature offrom 5 to 10° C.

As used herein, the term “diluent” refers to diluents in liquid formthat is in a liquid state, liquid at room temperature and preferablyliquid under the pressure conditions in the loop reactor. Diluents whichare suitable for being used in accordance with the present may comprisebut are not limited to hydrocarbon diluents such as aliphatic,cycloaliphatic and aromatic hydrocarbon solvents, or halogenatedversions of such solvents. The preferred solvents are C12 or lower,straight chain or branched chain, saturated hydrocarbons, C5 to C9saturated alicyclic or aromatic hydrocarbons or C2 to C6 halogenatedhydrocarbons. Non-limiting illustrative examples of solvents are butane,isobutane, pentane, hexane, heptane, cyclopentane, cyclohexane,cycloheptane, methyl cyclopentane, methyl cyclohexane, isooctane,benzene, toluene, xylene, chloroform, chlorobenzenes,tetrachloroethylene, dichloroethane and trichloroethane. In a preferredembodiment of the present invention, said diluent is isobutane. However,it should be clear from the present invention that other diluents may aswell be applied according to the present invention.

The term “co-monomer” refers to olefin co-monomers which are suitablefor being polymerized with olefin monomers, preferably ethylenemonomers. Co-monomers may comprise but are not limited to aliphaticC3-C20 alpha-olefins. Examples of suitable aliphatic C3-C20alpha-olefins include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene,1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene,1-octadecene and 1-eicosene. The term “co-polymer” refers to a polymer,which is made by linking two different types of in the same polymerchain. The term “homo-polymer” refers to a polymer which is made bylinking olefin (preferably ethylene) monomers, in the absence ofco-monomers.

The process of the invention uses a catalyst, preferably, aZiegler-Natta catalyst. As used herein, the “catalyst” refers to asubstance that causes a change in the rate of a polymerization reactionwithout itself being consumed in the reaction. In the present inventionit is especially applicable to catalysts suitable for the polymerizationof olefin to polyolefin and, in the present invention, it is especiallyapplicable to Ziegler-Natta catalysts. The term “Ziegler-Nattacatalysts” or “ZN catalysts” refers to catalysts preferably of thegeneral formula MX_(n), wherein M is a transition metal compoundselected from group IV to VII, wherein X is a halogen, and wherein n isthe valence of the metal. Preferably, M is a group IV, group V or groupVI metal, more preferably titanium, chromium or vanadium and mostpreferably titanium. Preferably, X is chlorine or bromine, and mostpreferably, chlorine. Illustrative examples of the transition metalcompounds comprise but are not limited to TiCl₃, TiCl₄. Preferred ZNcatalysts according to the invention are described in U.S. Pat. No.6,930,071 and U.S. Pat. No. 6,864,207, which are incorporated herein byreference.

As used herein, the term “catalyst slurry” refers to a compositioncomprising catalyst solid particles and a diluent. The solid particlescan be suspended in the diluent, either spontaneously or byhomogenization techniques, such as mixing. The solid particles can benon-homogeneously distributed in a diluent and form a sediment ordeposit.

Preferably, the catalyst is present with an average particle diameter(d50) smaller than 50 μm, and more preferably smaller than 25 μm,preferably smaller than 20 μm, most preferably smaller than 10 μm andpreferably larger than 3 μm. The d50 is measured by laser diffractionanalysis on a Malvern type analyser after having put the catalyst insuspension in cyclohexane. The d50 is defined as the particle size forwhich fifty percent by volume of the particles has a size lower than thed50. Malvern systems include the Malvern 2000, Malvern 2600 and Malvern3600 series. The Malvern MasterSizer may also be useful as it can moreaccurately measure the d50 towards the lower end of the range e.g. foraverage particle sizes of less 8 μm, by applying the theory of Mie,using appropriate optical models.

Preferably, the catalyst is fed into the loop reactor under diluentflushing (preferably isobutane flushing) at a rate of larger than 100kg/h, more preferably larger than 200 kg/h and preferably lower than 250kg/h. We have found that this leads to fewer blockage of the reactor,for instance at the catalyst feeding site.

Preferably, the catalyst is fed into the loop reactor with a velocity atleast 7 m/s, more preferably at least 10 m/s and preferably at most 40m/s. Surprisingly, we have found that this leads to fewer blockage ofthe reactor, for instance at the catalyst feeding site.

Preferably, the catalyst is fed into the loop reactor under diluentflushing at a rate of larger than 100 kg/h and with a velocity at least7 m/s.

Preferably, the catalyst is fed to the reactor in step b) in a catalystslurry at a concentration at the feeding site of lower than 1.0% byweight, more preferably lower than 0.8% by weight, and preferably higherthan 0.1% by weight. Surprisingly, this leads to fewer blockage problemsin the catalyst feeding lines and/or the catalyst slurry storage tank.

A preferred process according to the invention uses an activating agent.The term “activating agent” refers to materials that can be used inconjunction with a catalyst in order to improve the activity of thecatalyst during the polymerization reaction. In the present invention,it particularly refers to an organoaluminium compound, being optionallyhalogenated, having general formula AlR¹R²R³ or AlR¹R²Y, wherein R¹, R²,R³ is an alkyl having from 1 to 6 carbon atoms and R¹, R², R³ may be thesame or different and wherein Y is hydrogen or a halogen, as disclosedin U.S. Pat. No. 6,930,071 and U.S. Pat. No. 6,864,207, which areincorporated herein by reference. Preferred activating agents areTri-Ethyl Aluminum (TEAl), Tri-Iso-Butyl Aluminum (TIBAl), Tri-MethylAluminum (TMA), and Methyl-Methyl-Ethyl Aluminum (MMEAl). TEAl isparticularly preferred.

Preferably, the activating agent added to the loop reactor in aactivating agent slurry at a concentration of less than 90% by weight ofthe activating agent slurry composition, more preferably from 10 to 50%by weight, for instance around 20% by weight. Preferably, theconcentration of the activating agent in the loop reactor is lower than200 ppm, more preferably from 10 to 100 parts per million, mostpreferably from 20-70 ppm and for instance around 50 ppm.

According to one embodiment of the invention, the activating agent ispreferably fed at another site into the loop reactor as compared to thefeeding site of the catalyst and, more preferably, the catalyst is fedin the loop reactor at a distance (preferably upstream or downstream) tomeans for feeding the activating agent of at least 15%, more preferablyat least 20%, most preferably at least 25%, at least 30%, at least 40%of the length of the reactor path.

According to another embodiment of the invention, the catalyst and theactivating agent are preferably mixed before addition to the loopreactor. In that embodiment, the activating agent is referred as“preactivating agent”. In that embodiment, the combination of catalystand activating agent is preferably fed at the preferred location for thecatalyst, i.e. spatially separated from the pump and at a distanceupstream to the pump of at least 20%, more preferably at least 30%, mostpreferably at least 40%, more preferably at least 50%, at least 60%, atleast 70%, at least 80%, at least 90%, at least 95% of the length of thereactor path. The catalyst may be injected at any distance from at least20% upstream of the pump up to the outlet flange of the pump.

Particularly preferred catalyst for use in the present invention is aZiegler-Natta catalyst system comprising a Ziegler-Natta catalystcomponent D and a preactivating agent, wherein the Ziegler Nattacatalyst component D is obtainable by:

-   -   a) generating a reaction product A by contacting a magnesium        dialkoxide compound with a halogenating agent;    -   b) contacting reaction product A with a first        halogenating/titanating agent to form reaction product B;    -   c) contacting reaction product B with a second        halogenating/titanating agent to form reaction product C; and    -   d) contacting reaction product C with a third        halogenating/titanating agent to form catalyst component D.

Preferably the catalyst is made according to a process comprising thefollowing steps: a) contacting a magnesium dialkoxide compound with ahalogenating agent to form a reaction product A; b) contacting reactionproduct A with a first halogenating/titanating agent to form reactionproduct B; c) contacting reaction product B with a secondhalogenating/titanating agent to form reaction product C; and d)contacting reaction product C with a third halogenating/titanating agentto form reaction product D. The second and third halogenating/titanatingagents can comprise titanium tetrachloride. The second and thirdhalogenating/titanating steps can each comprise a titanium to magnesiumratio in the range of about 0.1 to 5. The reaction products A, B and Ccan each be washed with a hydrocarbon solvent prior to subsequenthalogenating/titanating steps. The reaction product D can be washed witha hydrocarbon solvent until titanium species [Ti] content is less thanabout 100 mmol/L.

In an embodiment, a method for making a catalyst component generallyincludes the steps of forming a metal dialkoxide from a metal dialkyland an alcohol, halogenating the metal dialkoxide to form a reactionproduct, contacting the reaction product with one or morehalogenating/titanating agent in three or more steps to form a catalystcomponent, and then treating the catalyst component with a preactivationagent such as an organoaluminum.

One embodiment of the method for making a catalyst can be generally asfollows:

M¹RR′+2R″OH→M¹(OR″)₂   1.

M¹(OR″)₂+ClAR′″_(x)→“A”  2.

“A”+TiCl₄/Ti(OR″″)₄→“B”  3.

“B”+TiCl₄→“C”;   4.

“C”+TiCl₄→“D”  5.

“D”+preactivating agent→catalyst   6.

In the above formulas, M¹ can be any suitable metal, usually a Group IIAmetal, typically Mg. In the above formulas, R, R′, R″, R′″, and R″″ areeach independently hydrocarbyl or substituted hydrocarbyl moieties, withR and R′ having from 1 to 20 carbon atoms, generally from 1 to 10 carbonatoms, typically from 2 to 6 carbon atoms, and can have from 2 to 4carbon atoms. R″ generally comprises from 3 to 20 carbon atoms, R′″generally comprises from 2-6 carbon atoms, and R″″ generally comprisesfrom 2-6 carbon atoms and is typically butyl. Any combination of two ormore of R, R′, R″, R′″, and R″″ can be used, may be the same, or thecombination of the R groups may be different from one another.

In the above embodiment comprising formula ClAR′″_(x), A is anon-reducing oxyphilic compound which is capable of exchanging onechloride for an alkoxide, R′″ is a hydrocarbyl or substitutedhydrocarbyl, and x is the valence of A minus 1. Examples of A includetitanium, silicon, aluminum, carbon, tin and germanium, typically istitanium or silicon wherein x is 3. Examples of R′″ include methyl,ethyl, propyl, isopropyl and the like having 2-6 carbon atoms. Nolimiting examples of a chlorinating agent that can be used in the methodare ClTi(O^(l)Pr)₃ and ClSi(Me)₃.

The metal dialkoxide of the above embodiment is chlorinated to form areaction product “A”. While the exact composition of product “A” isunknown, it is believed that it contains a partially chlorinated metalcompound, one example of which may be ClMg(OR″).

Reaction product “A” is then contacted with one or morehalogenating/titanating agent, such as for example a combination ofTiCl₄ and Ti(OBu)₄, to form reaction product “B”. Reaction product “B”which is probably a complex of chlorinated and partially chlorinatedmetal and titanium compounds. Reaction product “B” can comprise atitanium impregnated MgCl₂ support and for example, may possibly berepresented by a compound such as (MCl₂)_(y)(TiCl_(x)(OR)_(4-x))_(z).Reaction product “B” can be precipitated as a solid from the catalystslurry.

The second halogenation/titanation step produces reaction product, orcatalyst component, “C” which is also probably a complex of halogenatedand partially halogenated metal and titanium compounds but differentfrom “B” and may possibly be represented by(MCl₂)_(y)(TiCl_(x′)(OR)_(4-x′))_(z′). It is expected that the level ofhalogenation of “C” would be greater than that of product “B”. Thisgreater level of halogenation can produce a different complex ofcompounds.

The third halogenation/titanation step produces a reaction product, orcatalyst component, “D” which is also probably a complex of halogenatedand partially halogenated metal and titanium compounds but differentfrom “B” and “C”, and may possibly be represented by(MCl₂)_(y)(TiCl_(x″)(OR)_(4-x″))_(z″). It is expected that the level ofhalogenation of “D” would be greater than that of product “C”. Thisgreater level of halogenation would produce a different complex ofcompounds. While this description of the reaction products offers themost probable explanation of the chemistry at this time, the method isnot limited by this theoretical mechanism.

Metal dialkyls and the resultant metal dialkoxides suitable for use inthe method can include any that can be utilized in the method to yield asuitable polyolefin catalyst. These metal dialkoxides and dialkyls caninclude Group IIA metal dialkoxides and dialkyls. The metal dialkoxideor dialkyl can be a magnesium dialkoxide or dialkyl. Non-limitingexamples of suitable magnesium dialkyls include diethyl magnesium,dipropyl magnesium, dibutyl magnesium, butylethylmagnesium, etc.Butylethylmagnesium (BEM) is one suitable magnesiumdialkyl.

In the practice of the method, the metal dialkoxide can be a magnesiumcompound of the general formula Mg(OR″)₂ where R″ is a hydrocarbyl orsubstituted hydrocarbyl of 1 to 20 carbon atoms.

The metal dialkoxide can be soluble and is typically non-reducing. Anon-reducing compound has the advantage of forming MgCl₂ instead ofinsoluble species that can be formed by the reduction of compounds suchas MgRR′, which can result in the formation of catalysts having a broadparticle size distribution. In addition, Mg(OR″)₂, which is lessreactive than MgRR′, when used in a reaction involving chlorination witha mild chlorinating agent, followed by subsequenthalogenation/titanation steps, can result in a more uniform product,e.g., better catalyst particle size control and distribution.

Non-limiting examples of species of metal dialkoxides which can be usedinclude magnesium butoxide, magnesium pentoxide, magnesium hexoxide,magnesium di(2-ethylhexoxide), and any alkoxide suitable for making thesystem soluble.

As a non-limiting example, magnesium dialkoxide, such as magnesiumdi(2-ethylhexoxide), may be produced by reacting an alkyl magnesiumcompound (MgRR′) with an alcohol (ROH), as shown below.MgRR′+2R″OH→Mg(OR″)₂+RH+R′H

The reaction can take place at room temperature and the reactants form asolution. R and R′ may each be any alkyl group of 1-10 carbon atoms, andmay be the same or different. Suitable MgRR′ compounds include, forexample, diethyl magnesium, dipropyl magnesium, dibutyl magnesium andbutyl ethyl magnesium. The MgRR′ compound can be BEM, wherein RH and R′Hare butane and ethane, respectively.

In the practice of the method, any alcohol yielding the desired metaldialkoxide may be utilized. Generally, the alcohol utilized may be anyalcohol of the general formula R″OH where R″ is an alkyl group of 2-20carbon atoms, the carbon atoms can be at least 3, at least 4, at least5, or at least 6 carbon atoms. Non-limiting examples of suitablealcohols include ethanol, propanol, isopropanol, butanol, isobutanol,2-methyl-pentanol, 2-ethylhexanol, etc. While it is believed that almostany alcohol may be utilized, linear or branched, a higher order branchedalcohol, for example, 2-ethyl-1-hexanol, can be utilized.

The amount of alcohol added can vary, such as within a non-exclusiverange of 0 to 10 equivalents, is generally in the range of about 0.5equivalents to about 6 equivalents (equivalents are relative to themagnesium or metal compound throughout), and can be in the range ofabout 1 to about 3 equivalents.

Alkyl metal compounds can result in a high molecular weight species thatis very viscous in solution. This high viscosity may be reduced byadding to the reaction an aluminum alkyl such as, for example,triethylaluminum (TEAl), which can disrupt the association between theindividual alkyl metal molecules. The typical ratio of alkyl aluminum tometal can range from 0.001:1 to 1:1, can be 0.01 to 0.5:1 and also canrange from 0.03:1 to 0.2:1. In addition, an electron donor such as anether, for example, diisoamyl ether (DIAE), may be used to furtherreduce the viscosity of the alkyl metal. The typical ratio of electrondonor to metal ranges from 0:1 to 10:1 and can range from 0.1:1 to 1:1.

Agents useful in the step of halogenating the metal alkoxide include anyhalogenating agent which when utilized in the method will yield asuitable polyolefin catalyst. The halogenating step can be achlorinating step where the halogenating agent contains a chloride (i.e,is a chlorinating agent).

Halogenating of the metal alkoxide compound is generally conducted in ahydrocarbon solvent under an inert atmosphere. Non-limiting examples ofsuitable solvents include toluene, heptane, hexane, octane and the like.In this halogenating step, the mole ratio of metal alkoxide tohalogenating agent is generally in the range of about 6:1 to about 1:3,can be in the range of about 3:1 to about 1:2, can be in the range ofabout 2:1 to about 1:2, and can also be about 1:1.

The halogenating step is generally carried out at a temperature in therange of about 0° C. to about 100° C. and for a reaction time in therange of about 0.5 to about 24 hours. The halogenating step can becarried out at a temperature in the range of about 20° C. to about 90°C. and for a reaction time in the range of about 1 hour to about 4hours.

Once the halogenating step is carried out and the metal alkoxide ishalogenated, the halide product “A” can be subjected to two or morehalogenating/titanating treatments.

The halogenation/titanation agents utilized can be blends of twotetra-substituted titanium compounds with all four substituents beingthe same and the substituents being a halide or an alkoxide or phenoxidewith 2 to 10 carbon atoms, such as TiCl₄ or Ti(OR″″)₄. Thehalogenation/titanation agent utilized can be a chlorination/titanationagent.

The halogenation/titanation agent may be a single compound or acombination of compounds. The method provides an active catalyst afterthe first halogenation/titanation; however, there are desirably a totalof at least three halogenation/titanation steps.

The first halogenation/titanation agent is typically a mild titanationagent, which can be a blend of a titanium halide and an organictitanate. The first halogenation/titanation agent can be a blend ofTiCl₄ and Ti(OBu)₄ in a range from 0.5:1 to 6:1 TiCl₄/Ti(OBu)₄, theratio can be from 2:1 to 3:1 (“OBu” represents butoxide). It is believedthat the blend of titanium halide and organic titanate react to form atitanium alkoxyhalide, Ti(OR)_(a)X_(b), where OR and X are alkoxide andhalide, respectively and a+b is the valence of titanium, which istypically 4.

In the alternative, the first halogenation/titanation agent may be asingle compound. Examples of a first halogenation/titanation agent areTi(OC₂H₅)₃Cl, Ti(OC₂H₅)₂Cl₂, Ti(OC₃H₇)₂Cl₂, Ti(OC₃H₇)₃Cl, Ti(OC₄H₉)Cl₃,Ti(OC₆H₁₃)₂Cl₂, Ti(OC₂H₅)₂Br₂, and Ti(OC₁₂H₅)Cl₃.

The first halogenation/titanation step is generally carried out by firstslurrying the halogenation product “A” in a hydrocarbon solvent at roomtemperature/ambient temperature. No limiting examples of suitablehydrocarbons solvent include heptane, hexane, toluene, octane and thelike. The product “A” can be at least partially soluble in thehydrocarbon solvent.

A solid product “B” is precipitated at room temperature following theaddition of the halogenation/titanation agent to the soluble product“A”. The amount of halogenation/titanation agent utilized must besufficient to precipitate a solid product from the solution. In general,the amount of halogenation/titanation agent utilized, based on the ratioof titanium to metal, will generally be in the range of about 0.5 toabout 5, typically in the range of about 1 to about 4, and can be in therange about 1.5 to about 2.5. An example is TiCl₄/titanium (IV) butoxide(TNBT).

The solid product “B” precipitated in this first halogenation/titanationstep is then recovered by any suitable recovery technique, and thenwashed at room/ambient temperature with a solvent, such as hexane.Generally, the solid product “B” is washed until the [Ti] is less thanabout 100 mmol/L. Within the method [Ti] represents any titanium speciescapable of acting as a second generation Ziegler catalyst, which wouldcomprise titanium species that are not part of the reaction products asdescribed herein. The resulting product “B” is then subjected to asecond and third halogenating/titanating steps to produce products “C”and “D”. After each halogenating/titanating step the solid product canbe washed until the [Ti] is less than a desired amount. For example,less than about 100 mmol/L, less than about 50 mmol/L, or less thanabout 10 mmol/L. After the final halogenating/titanating step, theproduct can be washed until the [Ti] is less than a desired amount, forexample, less than about 20 mmol/L, less than about 10 mmol/L, or lessthan about 1.0 mmol/L. It is believed that a lower [Ti] can produceimproved catalyst results by reducing the amount of titanium that canact as a second generation Ziegler species. It is believed that a that alower [Ti] can be a factor in producing improved catalyst results suchas a narrower MWD.

The second halogenation/titanation step is generally carried out byslurrying the solid product recovered from the first titanation step,solid product “B”, in a hydrocarbon solvent. Hydrocarbon solvents listedas suitable for the first halogenation/titanation step may be utilized.The second and third halogenation/titanation steps can utilize adifferent compound or combination of compounds from the firsthalogenation/titanation step. The second and thirdhalogenation/titanation steps can utilize the same agent at aconcentration that is stronger than that used in the firsthalogenation/titanation agent, but this is not a necessity. The secondand third halogenating/titanating agents can be a titanium halide, suchas titanium tetrachloride (TiCl₄). The halogenation/titanation agent isadded to the slurry. The addition can be carried out at ambient/roomtemperature, but can also be carried out at temperatures and pressuresother than ambient.

Generally, the second and third halogenation/titanation agents comprisetitanium tetrachloride. Typically the second and thirdhalogenation/titanation steps each comprise a titanium to magnesiumratio in a range of about 0.1 to 5, a ratio of about 2.0 can also beused, and a ratio of about 1.0 can be used. The thirdhalogenation/titanation step is generally carried out at roomtemperature and in a slurry, but can also be carried out at temperaturesand pressures other than ambient.

The amount of titanium tetrachloride utilized, or alternatehalogenation/titanation agent, may also be expressed in terms ofequivalents, an equivalent herein is amount of titanium relative to themagnesium or metal compound. The amount of titanium of each of thesecond and third halogenating/titanating steps will generally be in therange of about 0.1 to about 5.0 equivalents, can be in the range ofabout 0.25 to about 4 equivalents, typically is in the range of about0.3 to about 3 equivalents, and it can be desirable to be in the rangeof about 0.4 to about 2.0 equivalents. In one particular embodiment, theamount of titanium tetrachloride utilized in each of the second andthird halogenation/titanation steps is in the range of about 0.45 toabout 1.5 equivalent.

The catalyst component “D” made by the above described process may becombined with an organometallic catalyst component (a “preactivatingagent”) to form a preactivated catalyst system suitable for thepolymerization of olefins. Typically, the preactivating agents which areused together with the transition metal containing catalyst component“D” are organometallic compounds such as aluminum alkyls, aluminum alkylhydrides, lithium aluminum alkyls, zinc alkyls, magnesium alkyls and thelike. Preferably, the preactivating agent is selected from the groupconsisting of trialkylaluminums, dialkylaluminum halides, andalkylaluminum dihalides.

The preactivating agent is preferably an organoaluminum compound. Theorganoaluminum preactivating agent is typically an aluminum alkyl of theformula AlR₃ wherein at least one R is an alkyl having 1-8 carbon atomsor a halide, and wherein each of the R may be the same or different.Suitable preactivating agents include trialkyl aluminum such as, forexample, trimethyl aluminum (TMA), triethylaluminum (TEAL),triisobutylaluminum (TIBAL) and also include diethylaluminum chloride,triisobutylaluminum chloride, butylaluminum dichloride, and the like,and mixtures thereof. The organoaluminum preactivating agent is morepreferably trimethyl aluminum (TMA), triethyl aluminum (TEAL),triisobutyl aluminum (TIBAL) or mixtures thereof. Preferably, thepreactivating agent is TEAL, since with TEAL the molecular weightdistribution (MWD) of the bimodal polyethylene prepared in the tworeactors in series is even wider than when using other organoaluminumpreactivating agents. Generally, when using TEAL as the preactivatingagent the MWD will be at least 5, preferably at least 6.

In general, the ratio of Al to titanium can be in the range from 0.1:1to 2:1 and typically is 0.25:1 to 1.2:1.

Optionally, the Ziegler-Natta catalyst may be pre-polymerized.Generally, a prepolymerization process is affected by contacting a smallamount of monomer with the catalyst after the catalyst has beencontacted with the preactivating agent. A pre-polymerization process isdescribed in U.S. Pat. Nos. 5,106,804; 5,153,158; and 5,594,071, herebyincorporated by reference.

Optionally, an electron donor may be added with the halogenation agent,the first halogenation/titanation agent, or the subsequenthalogenation/titanation agent or agents. It may be desirable to have anelectron donor utilized in the second halogenation/titanation step.Electron donors for use in the preparation of polyolefin catalysts arewell known, and any suitable electron donor may be utilized in themethod that will provide a suitable catalyst. Electron donors, alsoknown as Lewis bases, are organic compounds of oxygen, nitrogen,phosphorus, or sulfur which can donate an electron pair to the catalyst.

The electron donor may be a monofunctional or polyfunctional compound,can be selected from among the aliphatic or aromatic carboxylic acidsand their alkyl esters, the aliphatic or cyclic ethers, ketones, vinylesters, acryl derivatives, particularly alkyl acrylates or methacrylatesand silanes. An example of a suitable electron donor is di-n-butylphthalate. A generic example of a suitable electron donor is analkylsilylalkoxide of the general formula RSi(OR′)₃, e.g.,methylsilyltriethoxide [MeSi(OEt)₃], where R and R′ are alkyls with 1-5carbon atoms and may be the same or different. (“OEt” represents“ethoxy”)

For the polymerization process, an internal electron donor can be usedin the synthesis of the catalyst and an external electron donor orstereoselectivity control agent (SCA) to activate the catalyst atpolymerization. An internal electron donor may be used in the formationreaction of the catalyst during the halogenation orhalogenation/titanation steps. Compounds suitable as internal electrondonors for preparing conventional supported Ziegler-Natta catalystcomponents include ethers, diethers, ketones, lactones, electron donorscompounds with N, P and/or S atoms and specific classes of esters.Particularly suitable are the esters of phthalic acid, such asdiisobutyl, dioctyl, diphenyl and benzylbutylphthalate; esters ofmalonic acid, such as diisobutyl and diethylmalonate; alkyl andarylpivalates; alkyl, cycloalkyl and arylmaleates; alkyl and arylcarbonates such as diisobutyl, ethyl-phenyl and diphenylcarbonate;succinic acid esters, such as mono and diethyl succinate.

External donors which may be utilized in the preparation of a catalystinclude organosilane compounds such as alkoxysilanes of general formulaSiR_(m)(OR′)_(4-m), where R is selected from the group consisting of analkyl group, a cycloalkyl group, an aryl group and a vinyl group; R′ isan alkyl group; and m is 0-3, wherein R may be identical with R′; when mis 0, 1 or 2, the R′ groups may be identical or different; and when m is2 or 3, the R groups may be identical or different.

The external donor of the method can be selected from a silane compoundof the following formula: wherein R₁ and R₄ are both an alkyl orcycloalkyl group containing a primary, secondary or tertiary carbon atomattached to the silicon, R₁ and R₄ being the same or different; R₂ andR₃ are alkyl or aryl groups. R₁ may be methyl, isopropyl, cyclopentyl,cyclohexyl or t-butyl; R₂ and R₃ may be methyl, ethyl, propyl, or butylgroups and not necessarily the same; and R₄ may also methyl, isopropyl,cyclopentyl, cyclohexyl or t-butyl. Specific external donors arecyclohexylmethyldimethoxy silane (CMDS), diisopropyldimethoxysilane(DIDS) cyclohexyl isopropyl dimethoxysilane (CIDS),dicyclopentyldimethoxysilane (CPDS) or di-t-butyl dimethoxysilane(DTDS).

Preferably, the preactivating agent is an organoaluminium compound,preferably of the formula AlR₃, wherein R is an alkyl having 1-8 carbonatoms or a halide, and wherein each R may be the same or different. Morepreferably, the organoaluminium compound is TEAL.

Preferably, the halogenating agent is ClTi(OPr)₃.

Preferably, the first halogenating/titanating agent a mixture of TiCl₄and Ti(OBu)₄, in a molar ratio range of from 0.5:1 to 6:1 ofTiCl₄/Ti(OBu)₄. More preferably the molar ratio is 2:1 ofTiCl₄/Ti(OBu)₄.

Preferably, the second halogenating/titanating agent is TiCl₄.

Preferably, the third halogenating/titanating agent is also TiCl₄.

According to the invention, the polyolefin of the invention can beprepared by reacting olefin monomer in the presence of a catalyst in aloop reactor with a pump, wherein the catalyst is preferably fed intothe reactor spatially separated from said pump and at a distanceupstream to the pump of at least 20%, more preferably at least 25%, morepreferably at least 30%, for example at least 40%, for example at least50%, at least 60%, at least 70%, at least 80%, at least 90%, at least95%, of the length of the reactor path. The term “upstream” of the pump,refers to the direction opposite (against) the direction of the flow ofcirculation.

Preferably, the loop reactor consists of a plurality of interconnectedpipes, defining a reactor path. The terms “path” and “flow path” of thereactor are used herein as synonyms and are defined as the internalroute followed by the reactant stream and the formed polymer slurry inthe reactor.

Preferably, the reactor comprises at least one loop. More preferably,the reactor is connected to another loop reactor, creating a double loopreactor. Most preferably the reactor is connected in series with theother loop reactor, creating a double loop reactor connected in series.Reaction conditions are preferably different in each of said loopreactors. Polymerization reactors that can be connected in series, mayin particular be used to prepare polyolefin having different propertiesin the different reactors under different conditions. Preferably, theinvention relates to production of bimodal polyolefin with in twointerconnected loop reactors. Preferably, the reactor of the presentinvention is one of the reactors of a multi loop reactor, morepreferably a double loop reactor. Preferably, the reactor of theinvention is connected in series with at least one other loop reactors.The polyolefin may be produced in a second reactor, but is preferablyprepared in the first reactor. Following polymerization in the loopreactor of the invention (preferably into a bimodal polyolefin using twoloop reactors), the polyolefin is preferably dried and preferablyextruded into pellets.

The reactor path preferably has a length of from 80 to 140 meters, morepreferably 95 to 125 meter, for instance about 110 meter. Preferably thereactor path contains the polymer slurry comprising monomer, optionallyone or more co-monomer(s), a catalyst, optionally an activating agent,diluent and solid olefin polymer particles.

Preferably, the polymerization reaction is carried out at a temperatureof higher than 88° C., more preferably higher than 89° C. and preferablylower than 95° C. and most preferably lower than 92° C.

The reactor pressure is preferably held between 20 and 100 bar, 30 to 50bar, more preferably at pressure of 37 to 45 bar. In an embodiment, theslurry flow can be set between 5 and 15 m/s.

The reactor preferably contains means for feeding monomer and diluent inthe reactor. According to the invention, the reactor contain means forfeeding catalyst in the reactor. Optionally, means for feeding anactivating agent in the reactor are present. Preferably, the reactorfurther comprises a pump suitable for maintaining the polymer slurry incirculation in said reactor.

According to the invention, the means for feeding said catalyst in thereactor is spatially separated from the pump with a distance upstream tothe pump of at least 20% of the length of the reactor path, preferablyat least 30% and more preferably at least 50%. We have found thatspatially separating the means for catalyst feeding from the pump in thereactor, fewer blockages occur when producing polyolefin, particularlypolyethylene.

According to one embodiment of the invention, the catalyst andactivating agent are mixed before addition. According to anotherembodiment, the reactor contains means for feeding catalyst in thereactor that is spatially separated from the means for feeding theactivating agent with a distance upstream or downstream of at least 15%of the length of the reactor path, more preferably at least 20%, mostpreferably at least 40%. This allows a better control of the activity ofthe catalyst.

According to an embodiment, the catalyst is fed into a first loopreactor of a double loop reactor comprising a first loop reactorconnected in series to a second loop reactor.

FIG. 1 represents a loop reactor 100, consisting of a plurality ofinterconnected pipes 104. The vertical sections of the pipe segments 104are preferably provided with heat jackets 105. Polymerization heat canbe extracted by means of cooling water circulating in these jackets ofthe reactor. Reactants are introduced into the reactor 100 by line 107.Activation agent, may be injected in the reactor 100 by means of theline 106A. According to an embodiment of the invention, the catalyst isinjected in the reactor 100 by means of a line 106B which is provided ata distance upstream to the pump of at least 50% of the length of thereactor path. The polymerization slurry is directionally circulatedthroughout the loop reactor 100 as illustrated by the arrows 108 by oneor more pumps, such as axial flow pump 101. The pump may be powered byan electric motor 102. As used herein the term “pump” includes anydevice that raise the pressure of a fluid, by means for example of apiston or set of rotating impellers 103. Reactor 100 is further providedwith one or more settling legs 109 connected to the pipes 104 of thereactor 100. The settling legs 109 are preferably provided with anisolation valve 110. These valves 110 are open under normal conditionsand can be closed for example to isolate a settling leg from operation.Further, the settling legs can be provided with product take off ordischarge valves 111. The discharge valve 111 may be any type of valve,which can permit continuous or periodical discharge of polymer slurry,when it is fully open. Polymer slurry settled in the settling legs 109may be removed by means of one or more product recovery lines 113, e.g.to a product recovery zone or for instance to a second loop reactor.

FIG. 2 represents a double loop reactor with a first reactor 100connected in series to second reactor 116. The reactors comprise aplurality of interconnected pipes 104. The vertical sections of theinterconnected pipe segments 104 are preferably provided with heatjackets 105 to extract heat by means of cooling water. Reactants areintroduced into the reactor 100 by line 107. Activation agent may beinjected in the reactor 100 by means of the line 106A. According to anembodiment of the invention, the catalyst is injected in the reactor 100by means of a line 106B which is provided at a distance upstream to thepump of at least at least 50% of the length of the reactor path. Thepolymerization slurry is directionally circulated throughout the loopreactor 100 as illustrated by the arrows 108 by one or more pumps, suchas an axial flow pump 101. Pump 101 is powered by an electric motor 102,and comprises a set of rotating impellers 103. Reactor 100 is furtherprovided with one or more settling legs 109 connected to the pipes 104of the reactor 100.

The two loop reactors 100 and 116 are connected in series via thesettling legs 109 of the first loop reactor 100. It will be understoodthat while the loop reactor 100 is illustrated with four settling legs109, said loop reactor 100 may be equipped with less or more settlinglegs. The settling legs 109 of first loop reactor 100 are preferablyprovided with an isolation valve 110. Further, the settling legs can beprovided with discharge valves 111. Downstream the valve 111 at the exitof the settling leg 109 of said first reactor 100, a transfer line 112is provided which allows to transfer polymer slurry settled in thesettling leg 109 to the second reactor 116, preferably through a pistonvalve 115. These transfer lines 112 comprise generally cylindrical,intermediate product transfer lines. Along the transfer line 112, athree-way valve 114 may divert the flow to a product recovery zone ifthe multiple loop reactor has to be used in a parallel configuration.Reactants are introduced into the reactor 116 by line 107, and settledpolymer slurry from first reactor 100 by line 112 through valve 115. Thepolymerization slurry is directionally circulated throughout the secondloop reactor 116 as illustrated by the arrows 108 by axial flow pump101. Pump 101 is powered by an electric motor 102, and comprises a setof rotating impellers 103. The second reactor 116 is also provided withfour settling legs 109. It will be understood that while the loopreactor 116 is illustrated with four settling legs 109, said loopreactor 116 may be equipped with less or more settling legs. Thesettling legs 109 of second loop reactor 116 are preferably providedwith an isolation valve 110 and product take off or discharge valves111. Polymer slurry settled in the settling legs 109 of the secondreactor 116 may be removed by means of one or more product recoverylines 113 for instance to a product recovery zone.

Preferably, according to the present invention, the polyolefin reactorhas a pump and a catalyst line, wherein the catalyst line is located ata distance to the pump of at least 20%, more preferably at least 30%,most preferably at least 40% of the length of the reactor path.

The following non-limiting examples illustrate the invention:

EXAMPLES Example 1

A ZN catalyst slurry (0.7% by weight; d50 of 5 micron) was fed under200-240 kg/h isobutane (iC4) flushing into a double loop reactoraccording to FIG. 2 via line 106B at a distance from the pump ofapproximately 50% of the length distance of the reactor path. TEAlactivating agent (concentration of 20% by weight; at 50 ppm in thereactor) was fed with 100 kg/h iC4 in line 106A, located right beforepump 101. Ethylene monomer was fed at 5-10° C. The reactor temperaturewas kept at 90° C. The solid particle content of the polymer slurry inthe reactor was around 35% by weight.

Based on the above, the drawings, taking into account any constraints inPE production and with the objective of producing the polymers of theinvention, it will be understood that the skilled man can correctly setthe reactions conditions.

The loop reactor showed remarkable stability and no blockage of thereactor occurred. The polyethylene fluff from first reactor had an HLMIof 0.71 g/10 min and a density of 0.9413 g/cm³.

After polymerization in a second loop reactor and extrusion, bimodalpolymer pellets were obtained with a density of 0.959 g/cm³, thatcontained 47% of the polyethylene of the invention.

Example 2

The following polyethylene pellets were produced according to theprocess of Example 1 in which an activating agent was added. The HLMIand density are listed.

Catalyst ZN 5 μm ZN 5 μm ZN 5 μm Activating agent TEAI MMEAI TEAI HLMI(g/10 min) 24.5 30.2 22.3 density (g/cm³)  0.958  0.9586  0.9592

Example 3

Similar as to example 1, the following polymers were produced:

Use of ZN catalyst with a D50 of 5 μm (first run) led to a polyethylenefrom first reactor with HLMI of 0.11 g/10 min and density of 0.9355g/cm³. A second run with similar conditions and using a ZN catalyst withD50 of 5 μm (second run) led to polyethylene from first reactor withHLMI of 0.09 g/10 min and density of 0.9357 g/cm³.

After reaction in the second loop reactor and extrusion, bimodal polymerpellets were obtained with around 46% of polyethylene having an HLMI of6.6 g/10 min and density of 0.9556 g/cm³ for the ZN catalyst of D50 of 5μm (first run) and with around 46% by weight of the polyethylene havingan HLMI of 6.8 g/10 min and density of 0.9562 g/cm³ for the ZN catalystof D50 of 5 μm (second run).

1-12. (canceled)
 13. A loop reactor suitable for the polymerization ofolefin monomer, wherein said loop reactor comprises: a plurality ofinterconnected pipes defining a reactor path for a polymer slurry, saidpolymer slurry comprising monomer, a catalyst, solid olefin polymerparticles, optionally one or more co-monomer(s), optionally hydrogen,and optionally an activating agent; a line for feeding monomer,optionally one or more co-monomer(s) and optionally hydrogen into theloop reactor; a line for feeding catalyst into the loop reactor;optionally a line for feeding an activating agent into the loop reactor;and a pump suitable for maintaining the polymer slurry in circulation insaid loop reactor, characterized in that said line for feeding saidcatalyst into the loop reactor is spatially separated from the pump at adistance upstream to the pump of at least 20% of a length of the reactorpath.
 14. The loop reactor according to claim 13, wherein the line forfeeding said catalyst into the loop reactor is spatially separated fromthe line for feeding the activating agent by a distance upstream ordownstream of at least 15% of the length of the reactor path.
 15. Theloop reactor according to claim 13, wherein the loop reactor isconnected in series with another loop reactor.
 16. The loop reactoraccording to claim 13, wherein the line for feeding the catalyst in theloop reactor is spatially separated from the pump at a distance upstreamto the pump of at least 50% the length of the reactor path.
 17. The loopreactor according to claim 13, wherein the line for feeding the catalystin the loop reactor is spatially separated from the pump at a distanceupstream to the pump of at least 60% the length of the reactor path. 18.The loop reactor according to claim 13, wherein the length of thereactor path ranges from 80 to 140 meters.
 19. The loop reactoraccording to claim 13, wherein the catalyst has a median particle size(d50) smaller than 50 μm.
 20. The loop reactor according to claim 13,characterized in that the catalyst is fed into the loop reactor underdiluent flushing at a rate of larger than 100 kg/h and with a velocityat least 7 m/s.
 21. The loop reactor according to claim 13, wherein thecatalyst is in a catalyst slurry, and wherein the catalyst slurry is fedinto the loop reactor from a catalyst slurry storage tank.
 22. The loopreactor of claim 21, wherein a concentration of the catalyst in thecatalyst slurry at a feeding site into the loop reactor is lower than1.0% by weight.
 23. The loop reactor according to claim 13, wherein theloop reactor is a double loop reactor.
 24. The loop reactor according toclaim 23, wherein the double loop reactor comprises a first loop reactorconnected in series to a second loop reactor, and wherein the line forfeeding the catalyst into the loop reactor feeds the catalyst into thefirst loop reactor.
 25. A process of preparing polyolefin in a loopreactor comprising: feeding into the loop reactor olefin monomers,optionally one or more comonomers, and optionally hydrogen; feeding intothe loop reactor a catalyst and optionally an activating agent; andpolymerizing the olefin monomers to produce a polyolefin slurrycomprising solid polyolefin particles while circulating the polyolefinslurry through the loop reactor by means of a pump; characterized inthat the catalyst is fed into the loop reactor spatially separated fromthe pump at a distance upstream to the pump of at least 50% of a lengthof the reactor path.